Why does the German officer make the remark "It’s the fishes’ turn now!" in "Two...

Why does the German officer make the remark "It’s the fishes’ turn now!" in "Two Friends" by Guy de Maupassant ?

Monsieur Morissot and Monsieur Sauvage are captured, questioned, shot dead and thrown into the river. Here's a small excerpt:

A few streaks of blood flecked the surface of the river.The officer, calm throughout, remarked, with grim humour: ‘It’s the fishes’ turn now!’. Then he retraced his way to the house.

Does the officer mean to say the fish (in the river) can eat the men? Or does he mean it is the turn of the fish (the catch of Morissot and Sauvage) to die and be eaten? Please help if you understand that line.

In "Two Friends" by Guy de Maupassant, Monsieur Morissot and Monsieur Sauvage enjoy fishing. They have spent many pleasant days fishing. Now that the war is raging, the two French friends have not been fishing in a while. The two friends decide to take a risk and go fishing. With the enemy Germans nearby, Morissot and Sauvage are taking a chance at being caught.

No doubt, Morissot's and Sauvage's love for fishing outweighs any fears of being caught by the nearby German enemies. These two friends find a river bank and enjoy precious moments while waiting for the fish to bite. The two friends begin to catch fish. Tragically, the Germans spot the two friends and take them hostage.

The Germans demand the password that will allow them to enter Paris. Because Morissot and Sauvage will not give the password to the Germans, the two friends are shot and killed. The German soldiers tie rocks to the two friends' feet and throw them in the river. With a bit of grim humor, one of the German soldiers comments:

"It's the fishes' turn now!"

The German officer is being grim and sarcastic. He is pointing out that the fish will have their turn at Morissot and Sauvage. Morissot and Sauvage have had their turn at the fishes. Now, the German officer's comment is meant to be sarcastically humorous. When he relates that the fishes will have their turn, he is saying that Morissot and Sauvage will experience what the fishes experienced when the two friends were trying to catch and eat the fishes. It is the fishes' turn to enjoy catching and eating the men who enjoyed catching and eating the fishes.

It is not really funny, but the German officer is trying to be humorous.